1. Field of the Invention
The present invention relates to a thermal-transfer recording medium and a method using the thermal-transfer recording medium.
2. Discussion of the Background Art
When an image of a logistics label or a rated label and the like is formed on a transferring objective, such as a sheet, a film, etc., using a thermal-transfer method, for example, by transferring an ink from a thermal-transfer sheet, a certain printing energy is generally needed. A necessary amount of the printing energy varies depending upon density of an image, and a type and material of a transferring objective. When a surface of a sheet is rough and printing energy is insufficient, an image sometimes partially drops and decreases density. When a considerable amount of printing energy is applied, a thermal head of the thermal-transfer printer becomes significantly short life, and power is wasted even admitting successful transfer onto the rough surface. Further, there are certain demands for printing of considerable information on a limited area, recently. To meet such demands, small character and graphic should be precisely reproduced. However, when the printing energy is excessively applied, these character and graphic become thick and unreadable. Further, since a label attached to logistics and a nameplate or the like should bear friction, heat, and chemicals, an image thereof should have certain rigidity. However, a conventional thermal-transfer recording medium can neither form a fine image with small printing energy nor maintain rigidity of an image.
According to a widely spreading technology, sensitive printing is enabled by including wax in an ink layer as a main component and melting the wax with low energy. However, an image has poor image rigidity, such as abrasion proof, heat resistance, chemical resistance, etc. In contrast, a thermal-transfer sheet having an ink layer mainly including resin has excellent image rigidity. However, the thermal-transfer sheet cannot melt with low energy, thereby resulting in poor heat sensitivity.
Further, it is known that a thermal-transfer sheet mainly including resin employs polyether resin, such as a PET film, having an excellent transfer performance as a label.
For example, Japanese Patent Application Laid Open No. 10-95172 discusses a technology using polyether resin. The polyether resin has a monomer composition with a sulfonate-metallic base, a glass transition point of from 4 to 80 degree centigrade, and number average molecular weight of from 5000 to 25000. Japanese Patent Application Laid Open No. 10-230682 also discusses a technology using polyether resin. The polyether resin has ethylene oxide adduct of bisphenol-A as a monomer. Further, Japanese Patent Application Laid Open No. 2003-89276 discusses a technology using polyether resin. The polyether resin has a glass transition point (Tg) of from 50 to 100 degree centigrade, and number average molecular weight of from 1000 to 10000. Japanese Patent Application Laid Open No. 2003-103946 discusses a technology using more than two types of polyether resins having different number average molecular weights. Further, as discussed in Japanese Patent Application Laid Open No. 2001-171233, it is known that solubility, i.e., a performance of solving into solvent, is specified so as to significantly improve chemical resistance.
However, a thermal-transfer sheet mainly including the above-mentioned resin improve rigidity in a sense, but is still inferior in heat sensitivity in comparison with that mainly including wax. Then, molecular weight is significantly decreased as discussed in Japanese Patent Application Publication No. 4-34957, and such a technology has an excellent transferring performance with low energy, because molecular weight is decreased and solubility is preferable. However, such a technology tends to create thermal diffusion, and thus thin line, character, and graphic cannot precisely be reproduced. In short, it is difficult to validate all of heat sensitivity, image reproducibility, and image rigidity.